Magnetic random access memory element having tantalum perpendicular enhancement layer

ABSTRACT

The present invention is directed to a spin transfer torque (STT) MRAM device having a perpendicular magnetic tunnel junction (MTJ) memory element. The memory element includes a perpendicular MTJ structure in between a non-magnetic seed layer and a non-magnetic cap layer. The MTJ structure comprises a magnetic free layer structure and a magnetic reference layer structure with an insulating tunnel junction layer interposed therebetween, an anti-ferromagnetic coupling layer formed adjacent to the magnetic reference layer structure, and a magnetic fixed layer formed adjacent to the anti-ferromagnetic coupling layer. At least one of the magnetic free and reference layer structures includes a non-magnetic perpendicular enhancement layer, which improves the perpendicular anisotropy of magnetic layers adjacent thereto.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of the commonly assigned applicationbearing Ser. No. 14/053,231 filed on Oct. 14, 2013 by Gan et al. andentitled “Magnetic Random Access Memory Having Perpendicular EnhancementLayer,” which is a continuation-in-part of the commonly assignedapplication bearing Ser. No. 14/026,163 filed on Sep. 13, 2013 by Gan etal. and entitled “Perpendicular STTMRAM Device with Balanced ReferenceLayer,” which is a continuation-in-part of the commonly assignedapplication bearing Ser. No. 13/029,054 filed on Feb. 16, 2011 by Zhouet al. and entitled “Magnetic Random Access Memory With FieldCompensating Layer and Multi-Level Cell,” and a continuation-in-part ofthe commonly assigned application bearing Ser. No. 13/277,187 filed onOct. 19, 2011 by Yiming Huai et al., and entitled “Memory System HavingThermally Stable Perpendicular Magneto Tunnel Junction (MTJ) and AMethod of Manufacturing Same,” which claims priority to U.S. ProvisionalApplication No. 61/483,314. The present application is related to thecommonly assigned copending application bearing Ser. No. 13/737,897filed on Jan. 9, 2013, the commonly assigned copending applicationbearing Ser. No. 14/021,917 filed on Sep. 9, 2013, the commonly assignedcopending application bearing Ser. No. 13/099,321 filed on May 2, 2011,and the commonly assigned copending application bearing Ser. No.13/928,263.

BACKGROUND

The present invention relates to a magnetic random access memory (MRAM)device, and more particularly, to a spin transfer torque MRAM deviceincluding at least a perpendicular enhancement layer in its memoryelement.

Spin transfer torque magnetic random access memory (STT-MRAM) is a newclass of non-volatile memory, which can retain the stored informationwhen powered off. A STT-MRAM device normally comprises an array ofmemory cells, each of which includes at least a magnetic memory elementand a selection element coupled in series between appropriateelectrodes. Upon application of an appropriate voltage or current to themagnetic memory element, the electrical resistance of the magneticmemory element would change accordingly, thereby switching the storedlogic in the respective memory cell.

FIG. 1 shows a conventional memory element for a STT-MRAM devicecomprising a magnetic reference layer 50 and a magnetic free layer 52with an insulating tunnel junction layer 54 interposed therebetween,thereby collectively forming a magnetic tunneling junction (MTJ) 56. Themagnetic reference layer 50 and free layer 52 have magnetizationdirections 58 and 60, respectively, which are substantiallyperpendicular to the layer plane. Therefore, the MTJ 56 is aperpendicular type comprising the magnetic layers 50 and 52 withperpendicular anisotropy. Upon application of an appropriate currentthrough the perpendicular MTJ 56, the magnetization direction 60 of themagnetic free layer 52 can be switched between two directions: paralleland anti-parallel with respect to the magnetization direction 58 of themagnetic reference layer 50. The insulating tunnel junction layer 54 isnormally made of a dielectric material with a thickness ranging from afew to a few tens of angstroms. However, when the magnetizationdirections 60 and 58 of the magnetic free layer 52 and reference layer50 are substantially parallel, electrons polarized by the magneticreference layer 50 can tunnel through the insulating tunnel junctionlayer 54, thereby decreasing the electrical resistivity of theperpendicular MTJ 56. Conversely, the electrical resistivity of theperpendicular MTJ 56 is high when the magnetization directions 58 and 60of the magnetic reference layer 50 and free layer 52 are substantiallyanti-parallel. Accordingly, the stored logic in the magnetic memoryelement can be switched by changing the magnetization direction 60 ofthe magnetic free layer 52.

One of many advantages of STT-MRAM over other types of non-volatilememories is scalability. As the size of the perpendicular MTJ 56 isreduced, the current required to switch the magnetization direction 60of the magnetic free layer 52 is reduced accordingly, thereby reducingpower consumption. However, the thermal stability of the magnetic layers50 and 52, which is required for long term data retention, also degradeswith miniaturization of the perpendicular MTJ 56.

For the foregoing reasons, there is a need for a STT-MRAM device thathas a thermally stable perpendicular MTJ memory element and that can beinexpensively manufactured.

SUMMARY

The present invention is directed to a spin transfer torque (STT)magnetic random access memory (MRAM) device that satisfy this need. ASTT-MRAM device having features of the present invention comprises aplurality of memory cells with each including a selection transistorcoupled to a perpendicular MTJ memory element; a plurality of parallelword lines with each being coupled to a respective row of the selectiontransistors in a first direction; and a plurality of parallel bit lineswith each being coupled to a respective row of the memory elements in asecond direction perpendicular to the first direction; and optionally aplurality of parallel source lines with each being coupled to arespective row of the selection transistors in the first or seconddirection.

According to an aspect of the present invention as applied to aperpendicular MTJ memory element, the memory element includes a magnetictunnel junction (MTJ) structure in between a non-magnetic seed layer anda non-magnetic cap layer. The MTJ structure comprises a magnetic freelayer structure and a magnetic reference layer structure with aninsulating tunnel junction layer interposed therebetween, ananti-ferromagnetic coupling layer formed adjacent to the magneticreference layer structure, and a magnetic fixed layer formed adjacent tothe anti-ferromagnetic coupling layer. The magnetic free layer structureincludes a first magnetic free layer formed adjacent to the insulatingtunnel junction layer and a second magnetic free layer separated fromthe first magnetic free layer by a first non-magnetic perpendicularenhancement layer (PEL). The magnetic reference layer structure includesa first magnetic reference layer formed adjacent to the insulatingtunnel junction layer and a second magnetic reference layer separatedfrom the first magnetic reference layer by a second non-magneticperpendicular enhancement layer. The first and the second magnetic freelayers have respectively a first and a second variable magnetizationdirections substantially perpendicular to the layer plane thereof. Thefirst and second variable magnetization directions may be parallel oranti-parallel to each other. The first and second magnetic referencelayers have a first fixed magnetization direction substantiallyperpendicular to the layer plane thereof. The magnetic fixed layer has asecond fixed magnetization direction substantially opposite to the firstfixed magnetization direction.

According to another aspect of the present invention as applied to aperpendicular MTJ memory element, the memory element includes a magnetictunnel junction (MTJ) structure in between a non-magnetic seed layer anda non-magnetic cap layer. The MTJ structure comprises a magnetic freelayer structure and a magnetic reference layer structure with aninsulating tunnel junction layer interposed therebetween, a non-magnetictuning layer formed adjacent to the magnetic free layer structure, and amagnetic compensation layer formed adjacent to the non-magnetic tuninglayer. The magnetic free layer structure includes a first magnetic freelayer formed adjacent to the insulating tunnel junction layer and asecond magnetic free layer separated from the first magnetic free layerby a first non-magnetic perpendicular enhancement layer (PEL). Themagnetic reference layer structure includes a first magnetic referencelayer formed adjacent to the insulating tunnel junction layer and asecond magnetic reference layer separated from the first magneticreference layer by a second non-magnetic perpendicular enhancementlayer. The first and the second magnetic free layers have respectively afirst and a second variable magnetization directions substantiallyperpendicular to the layer plane thereof. The first and second variablemagnetization directions may be parallel or anti-parallel to each other.The first and second magnetic reference layers have a first fixedmagnetization direction substantially perpendicular to the layer planethereof. The magnetic compensation layer has a second fixedmagnetization direction substantially opposite to the first fixedmagnetization direction.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a schematic view of a conventional perpendicular magnetictunnel junction;

FIG. 2 is a schematic circuit diagram of a STT-MRAM device according toan embodiment of the present invention;

FIGS. 3A and 3B are schematic views of an embodiment of the presentinvention as applied to a perpendicular MTJ memory element;

FIGS. 4A and 4B are schematic views of another embodiment of the presentinvention as applied to a perpendicular MTJ memory element;

FIGS. 5A and 5B are schematic views of still another embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 6A and 6B are schematic views of yet another embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 7A and 7B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 8A and 8B are schematic views of yet still another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 9A and 9B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 10A and 10B are schematic views of yet still another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 11A and 11B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 12A and 12B are schematic views of embodiments of the presentinvention as applied to the perpendicular enhancement layer;

FIGS. 13A and 13B are schematic views of embodiments of the presentinvention as applied to the non-magnetic seed layer;

FIGS. 14A and 14B are schematic views of embodiments of the presentinvention as applied to the non-magnetic cap layer; and

FIGS. 15A and 15B are schematic views of embodiments of the presentinvention as applied to the non-magnetic tuning layer.

For purposes of clarity and brevity, like elements and components willbear the same designations and numbering throughout the Figures, whichare not necessarily drawn to scale.

DETAILED DESCRIPTION

In the Summary above and in the Detailed Description, and the claimsbelow, and in the accompanying drawings, reference is made to particularfeatures of the invention. It is to be understood that the disclosure ofthe invention in this specification includes all possible combinationsof such particular features. For example, where a particular feature isdisclosed in the context of a particular aspect or embodiment of theinvention, or a particular claim, that feature can also be used, to theextent possible, in combination with and/or in the context of otherparticular aspects and embodiments of the invention, and in theinvention generally.

Where reference is made herein to a material AB composed of element Aand element B, the material AB can be an alloy, a compound, or acombination thereof, except where the context excludes that possibility.

FIG. 2 is a schematic circuit diagram of a STT-MRAM device 100 accordingto an embodiment of the present invention. The STT-MRAM device 100comprises a plurality of memory cells 102, each of the memory cells 102including a selection transistor 104 coupled to a MTJ memory element106; a plurality of parallel word lines 108 with each being coupled to arespective row of the selection transistors 104 in a first direction;and a plurality of parallel bit lines 110 with each being coupled to arespective row of the memory elements 106 in a second directionperpendicular to the first direction; and optionally a plurality ofparallel source lines 112 with each being coupled to a respective row ofthe selection transistors 104 in the first or second direction.

The MTJ memory element 106 has a perpendicular MTJ structure thatincludes at least a perpendicular enhancement layer (PEL) to improve theperpendicular anisotropy of magnetic layers adjacent thereto. Anembodiment of the present invention as applied to a perpendicular MTJmemory element will now be described with reference to FIG. 3A.Referring now to FIG. 3A, the illustrated memory element 114 includes amagnetic tunnel junction (MTJ) structure 116 in between a non-magneticseed layer 118 and a non-magnetic cap layer 120. The MTJ structure 116comprises a magnetic free layer structure 122 and a magnetic referencelayer structure 124 with an insulating tunnel junction layer 126interposed therebetween. The magnetic reference layer structure 124 andthe magnetic free layer structure 122 are formed adjacent to thenon-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 122 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic free layer 130 separated from the first magnetic freelayer 128 by a first non-magnetic perpendicular enhancement layer (PEL)132. The magnetic reference layer structure 124 includes a firstmagnetic reference layer 134 formed adjacent to the insulating tunneljunction layer 126 and a second magnetic reference layer 136 separatedfrom the first magnetic reference layer 134 by a second non-magneticperpendicular enhancement layer 138. The first and the second magneticfree layers 128 and 130 have respectively a first and a second variablemagnetization directions 129 and 131 substantially perpendicular to thelayer plane thereof. The first and the second variable magnetizationdirections 129 and 131 may be parallel or anti-parallel to each other.The first and second magnetic reference layers 134 and 136 have a firstfixed magnetization direction 125 substantially perpendicular to thelayer plane thereof.

The stacking order of the individual layers in the MTJ structure 116 ofthe memory element 114 may be inverted without affecting the deviceperformance as illustrated in FIG. 3B. The memory element 114′ of FIG.3B has a MTJ structure 116′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 116. Accordingly,the magnetic free layer structure 122 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Another embodiment of the present invention as applied to a MTJ memoryelement is illustrated in FIG. 4A. The memory element 140 includes amagnetic tunnel junction (MTJ) structure 142 in between a non-magneticseed layer 118 and a non-magnetic cap layer 120. The MTJ structure 142comprises a magnetic free layer structure 122 and a magnetic referencelayer structure 144 with an insulating tunnel junction layer 126interposed therebetween. The magnetic reference layer structure 144 andthe magnetic free layer structure 122 are formed adjacent to thenon-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 122 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic free layer 130 separated from the first magnetic freelayer 128 by a non-magnetic perpendicular enhancement layer (PEL) 132.The first and the second magnetic free layers 128 and 130 haverespectively a first and a second variable magnetization directions 129and 131 substantially perpendicular to the layer plane thereof. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other. The magnetic reference layerstructure 144 has a fixed magnetization direction 145 substantiallyperpendicular to the layer plane thereof. The memory element 140 of FIG.4A is different from the memory element 114 of FIG. 3A in that themagnetic reference layer structure 144 is formed of a single magneticlayer.

The stacking order of the individual layers in the MTJ structure 142 ofthe memory element 140 may be inverted without affecting the deviceperformance as illustrated in FIG. 4B. The memory element 140′ of FIG.4B has a MTJ structure 142′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 142. Accordingly,the magnetic free layer structure 122 and the magnetic reference layerstructure 144 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Still another embodiment of the present invention as applied to a MTJmemory element is illustrated in FIG. 5A. The memory element 150includes a magnetic tunnel junction (MTJ) structure 152 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 152 comprises a magnetic free layer structure 154 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween. The magnetic reference layerstructure 124 and the magnetic free layer structure 154 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic reference layer structure 124 includes afirst magnetic reference layer 134 formed adjacent to the insulatingtunnel junction layer 126 and a second magnetic reference layer 136separated from the first magnetic reference layer 134 by a non-magneticperpendicular enhancement layer 138. The magnetic free layer structure154 has a variable magnetization direction 155 substantiallyperpendicular to the layer plane thereof. The first and second magneticreference layers 134 and 136 have a first fixed magnetization direction125 substantially perpendicular to the layer plane thereof. The memoryelement 150 of FIG. 5A is different from the memory element 114 of FIG.3A in that the magnetic free layer structure 154 is formed of a singlemagnetic layer.

The stacking order of the individual layers in the MTJ structure 152 ofthe memory element 150 may be inverted without affecting the deviceperformance as illustrated in FIG. 5B. The memory element 150′ of FIG.5B has a MTJ structure 152′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 152. Accordingly,the magnetic free layer structure 154 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

The non-magnetic seed layer 118 of the memory elements 114, 114′, 140,140′, 150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively,facilitates the optimal growth of the magnetic layer thereon to increaseperpendicular anisotropy. The non-magnetic seed layer 118 may alsoserves as a bottom electrode to the MTJ structures 116, 116′, 142, 142′,152, and 152′.

The non-magnetic cap layer 120 of the memory elements 114, 114′, 140,140′, 150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively,functions as a top electrode to the MTJ structures 116, 116′, 142, 142′,152, and 152′, but may also improve the perpendicular anisotropy of themagnetic layer adjacent thereto during annealing.

For the MTJ structures 116, 116′, 142, 142′, 152, and 152′ of FIGS. 3A,3B, 4A, 4B, 5A, and 5B, at least one of the magnetic free layerstructure 122 and the magnetic reference layer structure 124 includes anon-magnetic perpendicular enhancement layer 132 or 138 therein. Theperpendicular enhancement layers 132 and 138 further improve theperpendicular anisotropy of the magnetic layers adjacent thereto duringdeposition and annealing.

Yet another embodiment of the present invention as applied to a MTJmemory element is illustrated in FIG. 6A. The memory element 160includes a magnetic tunnel junction (MTJ) structure 162 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 162 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 124, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164. The magnetic fixed layerstructure 166 and the magnetic free layer structure 122 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic free layer structure 122 includes a firstmagnetic free layer 128 formed adjacent to the insulating tunneljunction layer 126 and a second magnetic free layer 130 separated fromthe first magnetic free layer 128 by a first non-magnetic perpendicularenhancement layer (PEL) 132. The magnetic reference layer structure 124includes a first magnetic reference layer 134 formed adjacent to theinsulating tunnel junction layer 126 and a second magnetic referencelayer 136 separated from the first magnetic reference layer 134 by asecond non-magnetic perpendicular enhancement layer 138. The first andthe second magnetic free layers 128 and 130 have respectively a firstand a second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer plane thereof. The first and the secondvariable magnetization directions 129 and 131 may be parallel oranti-parallel to each other. The first and second magnetic referencelayers 134 and 136 have a first fixed magnetization direction 125substantially perpendicular to the layer plane thereof. The magneticfixed layer 166 has a second fixed magnetization direction 167substantially opposite to the first fixed magnetization direction 125.The memory element 160 of FIG. 6A is different from the memory element114 of FIG. 3A in that the anti-ferromagnetic coupling layer 164 and themagnetic fixed layer 166 have been inserted in between the non-magneticseed layer 118 and the magnetic reference layer structure 124.

The stacking order of the individual layers in the MTJ structure 162 ofthe memory element 160 may be inverted without affecting the deviceperformance as illustrated in FIG. 6B. The memory element 160′ of FIG.6B has a MTJ structure 162′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 162. Accordingly,the magnetic free layer structure 122 and the magnetic fixed layerstructure 166 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 7A. The memory element 170includes a magnetic tunnel junction (MTJ) structure 172 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 172 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 144 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 144, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164. The magnetic fixed layerstructure 166 and the magnetic free layer structure 122 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic free layer structure 122 includes a firstmagnetic free layer 128 formed adjacent to the insulating tunneljunction layer 126 and a second magnetic free layer 130 separated fromthe first magnetic free layer 128 by a non-magnetic perpendicularenhancement layer (PEL) 132. The first and the second magnetic freelayers 128 and 130 have respectively a first and a second variablemagnetization directions 129 and 131 substantially perpendicular to thelayer plane thereof. The first and the second variable magnetizationdirections 129 and 131 may be parallel or anti-parallel to each other.The magnetic reference layer structure 144 has a first fixedmagnetization direction 145 substantially perpendicular to the layerplane thereof. The magnetic fixed layer 166 has a second fixedmagnetization direction 167 substantially opposite to the first fixedmagnetization direction 145. The memory element 170 of FIG. 7A isdifferent from the memory element 160 of FIG. 6A in that the magneticreference layer structure 144 is formed of a single magnetic layer.

The stacking order of the individual layers in the MTJ structure 172 ofthe memory element 170 may be inverted without affecting the deviceperformance as illustrated in FIG. 7B. The memory element 170′ of FIG.7B has a MTJ structure 172′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 172. Accordingly,the magnetic free layer structure 122 and the magnetic fixed layerstructure 166 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Yet still another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 8A. The memory element 180includes a magnetic tunnel junction (MTJ) structure 182 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 182 comprises a magnetic free layer structure 154 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 124, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164. The magnetic fixed layerstructure 166 and the magnetic free layer structure 122 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic reference layer structure 124 includes afirst magnetic reference layer 134 formed adjacent to the insulatingtunnel junction layer 126 and a second magnetic reference layer 136separated from the first magnetic reference layer 134 by a non-magneticperpendicular enhancement layer 138. The magnetic free layer structure154 has a variable magnetization direction 155 substantiallyperpendicular to the layer plane thereof. The first and second magneticreference layers 134 and 136 have a first fixed magnetization direction125 substantially perpendicular to the layer plane thereof. The magneticfixed layer 166 has a second fixed magnetization direction 167substantially opposite to the first fixed magnetization direction 125.The memory element 180 of FIG. 8A is different from the memory element160 of FIG. 6A in that the magnetic free layer structure 154 is formedof a single magnetic layer.

The stacking order of the individual layers in the MTJ structure 182 ofthe memory element 180 may be inverted without affecting the deviceperformance as illustrated in FIG. 8B. The memory element 180′ of FIG.8B has a MTJ structure 182′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 182. Accordingly,the magnetic free layer structure 154 and the magnetic fixed layerstructure 166 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, the MTJ structures 162,162′, 172, 172′, 182, and 182′ of FIGS. 6A, 6B, 7A, 7B, 8A, and 8B,respectively, have the magnetic fixed layer 166 anti-ferromagneticallycoupled to the reference layers 124 and 144 through theanti-ferromagnetic coupling layer 164. The magnetic fixed layer 166 isnot an “active” layer like the magnetic reference layer structure andthe magnetic free layer structure, which along with the tunnel junctionlayer 126 collectively form a MTJ that changes resistivity when aspin-polarized current pass therethrough. The main function of themagnetic fixed layer 166, which has an opposite magnetization directioncompared with the magnetic reference layer structures 124 and 144, is tocancel, as much as possible, the external magnetic field exerted by themagnetic reference layer structures 124 and 144 on the magnetic freelayer structures 122 and 154, thereby minimizing the offset field or netexternal field in the magnetic free layer structures 122 and 154.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 9A. The memory element 190includes a magnetic tunnel junction (MTJ) structure 192 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 192 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122, and amagnetic compensation layer 196 formed adjacent to the non-magnetictuning layer 194. The magnetic reference layer structure 124 and themagnetic compensation layer 196 are formed adjacent to the non-magneticseed layer 118 and cap layer 120, respectively. The magnetic free layerstructure 122 includes a first magnetic free layer 128 formed adjacentto the insulating tunnel junction layer 126 and a second magnetic freelayer 130 separated from the first magnetic free layer 128 by a firstnon-magnetic perpendicular enhancement layer (PEL) 132. The magneticreference layer structure 124 includes a first magnetic reference layer134 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic reference layer 136 separated from the first magneticreference layer 134 by a second non-magnetic perpendicular enhancementlayer 138. The first and the second magnetic free layers 128 and 130have respectively a first and a second variable magnetization directions129 and 131 substantially perpendicular to the layer plane thereof. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other. The first and secondmagnetic reference layers 134 and 136 have a first fixed magnetizationdirection 125 substantially perpendicular to the layer plane thereof.The magnetic compensation layer 196 has a second fixed magnetizationdirection 197 substantially opposite to the first fixed magnetizationdirection 125. The memory element 190 of FIG. 9A is different from thememory element 114 of FIG. 3A in that the non-magnetic tuning layer 194and the magnetic compensation layer 196 have been inserted in betweenthe magnetic free layer structure 122 and the non-magnetic cap layer120.

The stacking order of the individual layers in the MTJ structure 192 ofthe memory element 190 may be inverted without affecting the deviceperformance as illustrated in FIG. 9B. The memory element 190′ of FIG.9B has a MTJ structure 192′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 192. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Yet still another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 10A. The memory element 200includes a magnetic tunnel junction (MTJ) structure 202 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 202 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 144 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122, and amagnetic compensation layer 196 formed adjacent to the non-magnetictuning layer 194. The magnetic reference layer structure 144 and themagnetic compensation layer 196 are formed adjacent to the non-magneticseed layer 118 and cap layer 120, respectively. The magnetic free layerstructure 122 includes a first magnetic free layer 128 formed adjacentto the insulating tunnel junction layer 126 and a second magnetic freelayer 130 separated from the first magnetic free layer 128 by anon-magnetic perpendicular enhancement layer (PEL) 132. The first andthe second magnetic free layers 128 and 130 have respectively a firstand a second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer plane thereof. The first and the secondvariable magnetization directions 129 and 131 may be parallel oranti-parallel to each other. The magnetic reference layer structure 144has a first fixed magnetization direction 145 substantiallyperpendicular to the layer plane thereof. The magnetic compensationlayer 196 has a second fixed magnetization direction 197 substantiallyopposite to the first fixed magnetization direction 145. The memoryelement 200 of FIG. 10A is different from the memory element 190 of FIG.9A in that the magnetic reference layer structure 144 is formed of asingle magnetic layer.

The stacking order of the individual layers in the MTJ structure 202 ofthe memory element 200 may be inverted without affecting the deviceperformance as illustrated in FIG. 10B. The memory element 200′ of FIG.10B has a MTJ structure 202′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 202. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 144 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 11A. The memory element 210includes a magnetic tunnel junction (MTJ) structure 212 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 212 comprises a magnetic free layer structure 154 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122, and amagnetic compensation layer 196 formed adjacent to the non-magnetictuning layer 194. The magnetic reference layer structure 124 and themagnetic compensation layer 196 are formed adjacent to the non-magneticseed layer 118 and cap layer 120, respectively. The magnetic referencelayer structure 124 includes a first magnetic reference layer 134 formedadjacent to the insulating tunnel junction layer 126 and a secondmagnetic reference layer 136 separated from the first magnetic referencelayer 134 by a non-magnetic perpendicular enhancement layer 138. Themagnetic free layer structure 154 has a variable magnetization direction155 substantially perpendicular to the layer plane thereof. The firstand second magnetic reference layers 134 and 136 have a first fixedmagnetization direction 125 substantially perpendicular to the layerplane thereof. The magnetic compensation layer 196 has a second fixedmagnetization direction 197 substantially opposite to the first fixedmagnetization direction 125. The memory element 210 of FIG. 11A isdifferent from the memory element 190 of FIG. 9A in that the magneticfree layer structure 154 is formed of a single magnetic layer.

The stacking order of the individual layers in the MTJ structure 212 ofthe memory element 210 may be inverted without affecting the deviceperformance as illustrated in FIG. 11B. The memory element 210′ of FIG.11B has a MTJ structure 212′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 212. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, the MTJ structures 192,192′, 202, 202′, 212, and 212′ of FIGS. 9A, 9B, 10A, 10B, 11A, and 11B,respectively, have the magnetic compensation layer 196 separated fromthe magnetic free layer structures 122 and 154 by the non-magnetictuning layer 194. The magnetic compensation layer 196 is not an “active”layer like the magnetic reference layer structure and the magnetic freelayer structure, which along with the tunnel junction layer 126collectively form a MTJ that changes resistivity when a spin-polarizedcurrent pass therethrough. The main function of the magneticcompensation layer 196, which has an opposite magnetization directioncompared with the magnetic reference layer structures 124 and 144, is tocancel, as much as possible, the external magnetic field exerted by themagnetic reference layer structures 124 and 144 on the magnetic freelayer structures 122 and 154, thereby minimizing the offset field or netexternal field in the magnetic free layer structures 122 and 154.

For the MTJ memory elements 114, 114′, 140, 140′, 160, 160′, 170, 170′,190, 190′, 200, and 200′ of FIGS. 3A, 3B, 4A, 4B, 6A, 6B, 7A, 7B, 9A,9B, 10A, and 10B, respectively, where the magnetic free layer structure122 comprises the first and second magnetic free layers 128 and 130, thefirst and second magnetic free layers 128 and 130 each may be formed ofa magnetic material comprising cobalt (Co) and iron (Fe), such as butnot limited to cobalt-iron-boron (CoFeB), cobalt-iron-boron-titanium(CoFeBTi), cobalt-iron-boron-zirconium, (CoFeBZr),cobalt-iron-boron-hafnium (CoFeBHf), cobalt-iron-boron-vanadium(CoFeBV), cobalt-iron-boron-tantalum (CoFeBTa),cobalt-iron-boron-chromium (CoFeBCr), cobalt-iron-nickel (CoFeNi),cobalt-iron-titanium (CoFeTi), cobalt-iron-zirconium (CoFeZr),cobalt-iron-hafnium (CoFeHf), cobalt-iron-vanadium (CoFeV),cobalt-iron-niobium (CoFeNb), cobalt-iron-tantalum (CoFeTa),cobalt-iron-chromium (CoFeCr), cobalt-iron-molybdenum (CoFeMo),cobalt-iron-tungsten (CoFeW), cobalt-iron-aluminum (CoFeAl),cobalt-iron-silicon (CoFeSi), cobalt-iron-germanium (CoFeGe),cobalt-iron-phosphorous (CoFeP), or any combination thereof. For the MTJmemory elements 150, 150′, 180, 180′, 210, and 210′ of FIGS. 5A, 5B, 8A,8B, 11A, and 11B, respectively, where the magnetic free layer structure154 has a single magnetic layer, the magnetic free layer structure 154may comprise a magnetic material comprising Co and Fe, such as but notlimited to CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV, CoFeBTa, CoFeBCr,CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa, CoFeCr, CoFeMo,CoFeW, CoFeAl, CoFeSi, CoFeGe, CoFeP, or any combination thereof.

For the MTJ memory elements 114, 114′, 150, 150′, 160, 160′, 180, 180′,190, 190′, 210, and 210′ of FIGS. 3A, 3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A,9B, 11A, and 11B, respectively, where the magnetic reference layerstructure 124 comprises the first and second magnetic reference layers134 and 136, the first and second magnetic reference layers 134 and 136each may be formed of a magnetic material comprising Co and Fe, such asbut not limited to CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV, CoFeBTa,CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa, CoFeCr,CoFeMo, CoFeW, CoFeAl, CoFeSi, CoFeGe, CoFeP, or any combinationthereof. Moreover, the second magnetic reference layer 136 may also havea magnetic superlattice structure comprising repeated alternating layersof two or more materials, such as but not limited to (Co/Pt)_(n),(Co/Pd)_(n), (Co/Ni)_(n), (CoFe/Pt)_(n), (Co/Pt(Pd))_(n), or anycombination thereof. Alternatively, the second magnetic reference layer136 may be formed of a magnetic material comprising Co and Cr, such asbut not limited to CoCr, CoCrB, CoCrPt, CoCrPtB, CoCrPd, CoCrTi, CoCrZr,CoCrHf, CoCrV, CoCrNb, CoCrTa, or any combination thereof. For the MTJmemory elements 140, 140′, 170, 170′, 200, and 200′ of FIGS. 4A, 4B, 7A,7B, 10A, and 10B, respectively, where the magnetic reference layerstructure 144 comprise a magnetic layer, the magnetic reference layerstructure 144 may be formed of a magnetic material comprising Co and Fe,such as but not limited to CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV,CoFeBTa, CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa,CoFeCr, CoFeMo, CoFeW, CoFeAl, CoFeSi, CoFeGe, CoFeP, or any combinationthereof.

For the perpendicular MTJ memory elements 160, 160′, 170, 170′, 180 and180′ of FIGS. 6A, 6B, 7A, 7B, 8A, and 8B, respectively, the magneticfixed layer 166 may be formed of a magnetic material comprising Co andFe, such as but not limited to CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV,CoFeBTa, CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa,CoFeCr, CoFeMo, CoFeW, CoFeAl, CoFeSi, CoFeGe, CoFeP, or any combinationthereof. Moreover, the magnetic fixed layer 166 may also have a magneticsuperlattice structure comprising repeated alternating layers of two ormore materials, such as but not limited to (Co/Pt)_(n), (Co/Pd)_(n),(Co/Ni)_(n), (CoFe/Pt)_(n), (Co/Pt(Pd))_(n), or any combination thereof.Alternatively, the magnetic fixed layer 166 may be formed of a magneticmaterial comprising Co and Cr, such as but not limited to CoCr, CoCrB,CoCrPt, CoCrPtB, CoCrPd, CoCrTi, CoCrZr, CoCrHf, CoCrV, CoCrNb, CoCrTa,or any combination thereof. The anti-ferromagnetic coupling layer 164,which couples the magnetic fixed layer 166 to the magnetic referencelayer structures 124 and 144, is made of ruthenium (Ru) or tantalum(Ta).

For the perpendicular MTJ memory elements 190, 190′, 200, 200′, 210 and210′ of FIGS. 9A, 9B, 10A, 10B, 11A, and 11B, respectively, the magneticcompensation layer 196 may be formed of a magnetic material comprisingCo and Fe, such as but not limited to CoFeB, CoFeBTi, CoFeBZr, CoFeBHf,CoFeBV, CoFeBTa, CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb,CoFeTa, CoFeCr, CoFeMo, CoFeW, CoFeAl, CoFeSi, CoFeGe, CoFeP, or anycombination thereof. Moreover, the magnetic compensation layer 196 mayalso have a magnetic superlattice structure comprising repeatedalternating layers of two or more materials, such as but not limited to(Co/Pt)_(n), (Co/Pd)_(n), (Co/Ni)_(n), (CoFe/Pt)_(n), (Co/Pt(Pd))_(n),or any combination thereof. Alternatively, the magnetic compensationlayer 196 may be formed of a magnetic material comprising Co and Cr,such as but not limited to CoCr, CoCrB, CoCrPt, CoCrPtB, CoCrPd, CoCrTi,CoCrZr, CoCrHf, CoCrV, CoCrNb, CoCrTa, or any combination thereof.

The insulating tunnel junction layer 126 for all perpendicular MTJelements of FIGS. 3A-11A and 3B-11B may be formed of an insulatingmaterial, such as but not limited to magnesium oxide (MgO) or aluminumoxide (AlO_(x)).

The perpendicular enhancement layer (PEL) 132 in the magnetic free layerstructure 122 of FIGS. 3A, 3B, 4A, 4B, 6A, 6B, 7A, 7B, 9A, 9B, 10A, and10B may be formed of any suitable non-magnetic material. In anembodiment, the PEL 132 is formed of a PEL oxide, such as but notlimited to magnesium oxide (MgO) titanium oxide (TiOx), zirconium oxide(ZrOx), hafnium oxide (HfOx), vanadium oxide (VOx), niobium oxide(NbOx), tantalum oxide (TaOx), chrome oxide (CrOx), molybdenum oxide(MoOx), tungsten oxide (WOx), rhodium oxide (RhOx), nickel oxide (NiOx),palladium oxide (PdOx), platinum oxide (PtOx), copper oxide (CuOx),silver oxide (AgOx), ruthenium oxide (RuOx), silicon oxide (SiOx), orany combination thereof.

In another embodiment, the PEL is formed of a PEL nitride, such as butnot limited to titanium nitride (TiNx), zirconium nitride (ZrNx),hafnium nitride (HfNx), vanadium nitride (VNx), niobium nitride (NbNx),tantalum nitride (TaNx), chrome nitride (CrNx), molybdenum nitride(MoNx), tungsten nitride (WNx), nickel nitride (NiNx), palladium nitride(PdNx), platinum oxide (PtOx), ruthenium nitride (RuNx), silicon nitride(SiNx), or any combination thereof.

In still another embodiment, the PEL 132 is formed of a PEL oxynitride,such as but not limited to titanium oxynitride (TiOxNy), zirconiumoxynitride (ZrOxNy), hafnium oxynitride (HfOxNy), vanadium oxynitride(VOxNy), niobium oxynitride (NbOxNy), tantalum oxynitride (TaOxNy),chrome oxynitride (CrOxNy), molybdenum oxynitride (MoOxNy), tungstenoxynitride (WOxNy), nickel oxynitride (NiOxNy), palladium oxynitride(PdOxNy), platinum oxyoxide (PtOxNy), ruthenium oxynitride (RuOxNy),silicon oxynitride (SiOxNy) or any combination thereof.

In yet another embodiment, the PEL 132 is formed of a PEL rutheniumoxide based material comprising ruthenium, oxygen, and at least oneother element, such as but not limited to TiRuOx, ZrRuOx, HfRuOx, VRuOx,NbRuOx, TaRuOx, CrRuOx, MoRuOx, WRuOx, RhRuOx, NiRuOx, PdRuOx, PtRuOx,CuRuOx, AgRuOx, or any combination thereof.

In still yet another embodiment, the PEL 132 is formed of a PEL metallicmaterial such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Rh, Pd, Pt, Cu, Ag,or any combination thereof. The PEL metallic material may also includenon-magnetic alloys comprising one or more magnetic elements and one ormore non-magnetic elements, such as but not limited to CoTi, CoZr, CoHf,CoV, CoNb, CoTa, CoFeTa, CoCr, CoMo, CoW, NiCr, NiTi, CoNiCr, CoNiTi, orany combination thereof. For these non-magnetic alloys containingmagnetic elements, the content of the magnetic elements is below thethreshold required for becoming magnetized. Alternatively, the PELmetallic material may also include nominally magnetic materials, such asCoFeB, that have extreme thin thickness, thereby rendering the nominallymagnetic materials non-magnetic. For example, CoFeB becomes non-magneticwhen the thickness thereof is less than about 0.7 nm.

The PEL 132 may include one or more sublayers therein. In an embodiment,the PEL 132 may include a first PEL sublayer 310 and a second PELsublayer 312 as illustrated in FIG. 12A. The first and second PELsublayers 310 and 312 each is formed of the above-described PEL oxide,PEL nitride, PEL oxynitride, PEL ruthenium oxide based material, or PELmetallic material. The first PEL sublayer 310 may form adjacent to thefirst magnetic free layer 128 or the second magnetic free layer 130. Inanother embodiment, the PEL 132 may include a first PEL sublayer 320, asecond PEL sublayer 322, and a third PEL sublayer 324 as illustrated inFIG. 12B. The first, second, and third PEL sublayers 320-324 each may beformed of the above-described PEL oxide, PEL nitride, PEL oxynitride,PEL ruthenium oxide based material, or PEL metallic material. The firstPEL sublayer 320 may form adjacent to the first magnetic free layer 128or the second magnetic free layer 130.

The perpendicular enhancement layer (PEL) 138 in the magnetic referencelayer structure 124 of FIGS. 3A, 3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B,11A, and 11B may include one or more sublayers therein. In anembodiment, the PEL 138 is formed of the above-described PEL oxide, PELnitride, PEL oxynitride, PEL ruthenium oxide based material, or PELmetallic material. In another embodiment, the PEL layer 138 includes afirst PEL sublayer 310 and a second PEL sublayer 312 as illustrated inFIG. 12A. The first and second PEL sublayers 310 and 312 each is formedof the above-described PEL oxide, PEL nitride, PEL oxynitride, PELruthenium oxide based material, or PEL metallic material. The first PELsublayer 310 may form adjacent to the first magnetic reference layer 134or the second magnetic reference layer 136. In still another embodiment,the PEL layer 138 includes a first PEL sublayer 320, a second PELsublayer 322, and a third PEL sublayer 324 as illustrated in FIG. 12B.The first, second, and third PEL sublayers 320-324 each is formed of theabove-described PEL oxide, PEL nitride, PEL oxynitride, PEL rutheniumoxide based material, or PEL metallic material. The first PEL sublayer320 may form adjacent to the first magnetic reference layer 134 or thesecond magnetic reference layer 136.

The non-magnetic seed layer 118 of FIGS. 3-11A and 3-11B may include oneor more sublayers therein. In an embodiment, the non-magnetic seed layer118 is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. In another embodiment, the non-magnetic seed layer 118includes a first seed sublayer 410 and a second seed sublayer 412 asillustrated in FIG. 13A. The first and second seed sublayers 410 and 412each is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. The first seed sublayer 410 or the second seed sublayer 412may form adjacent to one of the magnetic layer structures 122, 124, 144,and 154. In still another embodiment, the non-magnetic seed layer 118includes a first seed sublayer 420, a second seed sublayer 422, and athird seed sublayer 424 as illustrated in FIG. 13B. The first, second,and third seed sublayers 420-424 each is formed of the above-describedPEL oxide, PEL nitride, PEL oxynitride, PEL ruthenium oxide basedmaterial, or PEL metallic material. The first seed sublayer 420 or thethird seed sublayer 424 may form adjacent to one of the magnetic layerstructures 122, 124, 144, and 154.

The non-magnetic cap layer 120 of FIGS. 3-11A and 3-11B may include oneor more sublayers therein. In an embodiment, the non-magnetic cap layer120 is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. In another embodiment, the non-magnetic cap layer 120 includesa first cap sublayer 510 and a second cap sublayer 512 as illustrated inFIG. 14A. The first and second cap sublayers 510 and 512 each is formedof the above-described PEL oxide, PEL nitride, PEL oxynitride, PELruthenium oxide based material, or PEL metallic material. The first capsublayer 510 or the second cap sublayer 512 may form adjacent to one ofthe magnetic layer structures 122, 124, 144, and 154. In still anotherembodiment, the non-magnetic cap layer 120 includes a first cap sublayer520, a second cap sublayer 522, and a third cap sublayer 524 asillustrated in FIG. 14B. The first, second, and third cap sublayers520-524 each is formed of the above-described PEL oxide, PEL nitride,PEL oxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. The first cap sublayer 520 or the third cap sublayer 524 mayform adjacent to one of the magnetic layer structures 122, 124, 144, and154.

The non-magnetic tuning layer 194 of FIGS. 9-11A and 9-11B may includeone or more sublayers therein. In an embodiment, the non-magnetic tuninglayer 194 is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. In another embodiment, the non-magnetic tuning layer 194includes a first tuning sublayer 610 and a second tuning sublayer 612 asillustrated in FIG. 15A. The first and second tuning sublayers 610 and612 each is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. The first tuning sublayer 610 or the second tuning sublayer612 may form adjacent to the magnetic compensation layer 196. In stillanother embodiment, the non-magnetic tuning layer 194 includes a firsttuning sublayer 620, a second tuning sublayer 622, and a third tuningsublayer 624 as illustrated in FIG. 15B. The first, second, and thirdtuning sublayers 620-624 each is formed of the above-described PELoxide, PEL nitride, PEL oxynitride, PEL ruthenium oxide based material,or PEL metallic material. The first tuning sublayer 620 or the thirdtuning sublayer 624 may form adjacent to the magnetic compensation layer196.

The previously described embodiments of the present invention have manyadvantages, including high perpendicular anisotropy and minimum offsetfield. It is important to note, however, that the invention does notrequire that all the advantageous features and all the advantages needto be incorporated into every embodiment of the present invention.

While the present invention has been shown and described with referenceto certain preferred embodiments, it is to be understood that thoseskilled in the art will no doubt devise certain alterations andmodifications thereto which nevertheless include the true spirit andscope of the present invention. Thus the scope of the invention shouldbe determined by the appended claims and their legal equivalents, ratherthan by examples given.

What is claimed is:
 1. A magnetic random access memory device comprisinga plurality of memory elements, each of said memory elements including amagnetic tunnel junction (MTJ) structure in between a non-magnetic seedlayer and a non-magnetic cap layer, said MTJ structure comprising amagnetic free layer structure and a magnetic reference layer structurewith an insulating tunnel junction layer interposed therebetween,wherein said magnetic reference layer structure includes a firstmagnetic reference layer formed adjacent to said insulating tunneljunction layer and a second magnetic reference layer separated from saidfirst magnetic reference layer by a first non-magnetic perpendicularenhancement layer with said first and second magnetic reference layershaving a first fixed magnetization direction substantially perpendicularto layer planes thereof, said magnetic free layer structure includes twomagnetic free layers with a second non-magnetic perpendicularenhancement layer interposed therebetween, said two magnetic free layershaving variable magnetization directions that are substantiallyperpendicular to layer planes thereof and are parallel to each other. 2.The magnetic random access memory device according to claim 1, furthercomprising: a plurality of selection transistors, each of said selectiontransistors being coupled to a respective one of said memory elements tocollectively form a memory cell; a plurality of parallel word lines,each of said word lines being coupled to gates of a respective row ofsaid selection transistors in a first direction; and a plurality ofparallel bit lines, each of said bit lines being coupled to a respectiverow of said memory elements in a second direction perpendicular to saidfirst direction.
 3. The magnetic random access memory device accordingto claim 1, wherein one of said two magnetic free layers having saidvariable magnetization directions that are substantially perpendicularto said layer planes thereof is made of CoFeB.
 4. The magnetic randomaccess memory device according to claim 3, wherein the other one of saidtwo magnetic free layers having said variable magnetization directionsthat are substantially perpendicular to said layer planes thereof ismade of CoFe.
 5. The magnetic random access memory device according toclaim 3, wherein the other one of said two magnetic free layers havingsaid variable magnetization directions that are substantiallyperpendicular to said layer planes thereof is made of CoFeTa.
 6. Themagnetic random access memory device according to claim 1, wherein oneof said two magnetic free layers is formed adjacent to said insulatingtunnel junction layer and is made of CoFeB, the other one of said twomagnetic free layers is made of CoFe.
 7. The magnetic random accessmemory device according to claim 6, wherein said second non-magneticperpendicular enhancement layer includes a metallic layer made oftungsten, hafnium, tantalum, molybdenum, zirconium, niobium, or anycombination thereof.
 8. The magnetic random access memory deviceaccording to claim 1, wherein said non-magnetic cap layer, formedadjacent to one of said two magnetic free layers having said variablemagnetization directions that are substantially perpendicular to saidlayer planes thereof, includes an insulating layer that comprisesmagnesium and oxygen.
 9. The magnetic random access memory deviceaccording to claim 1, wherein said first magnetic reference layercomprises cobalt, iron, and boron.
 10. The magnetic random access memorydevice according to claim 1, wherein said first non-magneticperpendicular enhancement layer includes a metallic layer made oftungsten, hafnium, tantalum, molybdenum, zirconium, niobium, or anycombination thereof.
 11. The magnetic random access memory deviceaccording to claim 1, wherein said second magnetic reference layer has amultilayer structure formed by interleaving layers of a first materialwith layers of a second material, at least one of said first and secondmaterials being magnetic.
 12. The magnetic random access memory deviceaccording to claim 11, wherein said first material is Co or CoFe, saidsecond material is Pt, Pd, Ni, or any combination thereof.
 13. Themagnetic random access memory device according to claim 1, wherein saidMTJ structure further comprises: a tuning layer formed adjacent to saidmagnetic free layer structure; and a magnetic compensation layer formedadjacent to said tuning layer, said magnetic compensation layer having asecond fixed magnetization direction substantially opposite to saidfirst fixed magnetization direction.
 14. The magnetic random accessmemory device according to claim 1, wherein said MTJ structure furthercomprises: an anti-ferromagnetic coupling layer formed adjacent to saidsecond magnetic reference layer; and a magnetic fixed layer formedimmediately adjacent to said anti-ferromagnetic coupling layer, saidmagnetic fixed layer having a second fixed magnetization directionsubstantially opposite to said first fixed magnetization direction. 15.The magnetic random access memory device according to claim 14, whereinsaid magnetic fixed layer has a multilayer structure formed byinterleaving layers of a first material with layers of a secondmaterial, at least one of said first and second materials beingmagnetic.
 16. The magnetic random access memory device according toclaim 14, wherein said first material is Co or CoFe, said secondmaterial is Pt, Pd, Ni, or any combination thereof.
 17. The magneticrandom access memory device according to claim 16, wherein saidnon-magnetic seed layer is formed adjacent to said magnetic fixed layerand includes a metallic layer made of NiTa or NiTi.
 18. A magneticrandom access memory device comprising a plurality of memory elements,each of said memory elements including a magnetic tunnel junction (MTJ)structure in between a non-magnetic seed layer and a non-magnetic caplayer, said MTJ structure comprising: a magnetic free layer structureand a magnetic reference layer structure with an insulating tunneljunction layer interposed therebetween, said magnetic reference layerstructure including a first magnetic reference layer formed adjacent tosaid insulating tunnel junction layer and a second magnetic referencelayer separated from said first magnetic reference layer by a firstnon-magnetic perpendicular enhancement layer with said first and secondmagnetic reference layers having a first fixed magnetization directionsubstantially perpendicular to layer planes thereof, said magnetic freelayer structure including one or more magnetic free layers having avariable magnetization direction substantially perpendicular to layerplanes thereof; a tuning layer formed adjacent to said magnetic freelayer structure; and a magnetic compensation layer formed adjacent tosaid tuning layer, said magnetic compensation layer having a secondfixed magnetization direction substantially opposite to said first fixedmagnetization direction, wherein said tuning layer includes aninsulating layer that comprises magnesium and oxygen.
 19. A magneticrandom access memory device comprising a plurality of memory elements,each of said memory elements including a magnetic tunnel junction (MTJ)structure in between a non-magnetic seed layer and a non-magnetic caplayer, said MTJ structure comprising: a magnetic free layer structureand a magnetic reference layer structure with an insulating tunneljunction layer interposed therebetween, said magnetic reference layerstructure including a first magnetic reference layer formed adjacent tosaid insulating tunnel junction layer and a second magnetic referencelayer separated from said first magnetic reference layer by a firstnon-magnetic perpendicular enhancement layer with said first and secondmagnetic reference layers having a first fixed magnetization directionsubstantially perpendicular to layer planes thereof, said magnetic freelayer structure including one or more magnetic free layers having avariable magnetization direction substantially perpendicular to layerplanes thereof; a tuning layer formed adjacent to said magnetic freelayer structure; and a magnetic compensation layer formed adjacent tosaid tuning layer, said magnetic compensation layer having a secondfixed magnetization direction substantially opposite to said first fixedmagnetization direction, wherein said magnetic compensation layer has amultilayer structure formed by interleaving layers of a first materialwith layers of a second material, at least one of said first and secondmaterials being magnetic.
 20. The magnetic random access memory deviceaccording to claim 19, wherein said first material is Co or CoFe, saidsecond material is Pt, Pd, Ni, or any combination thereof.